1. Field of the Invention
The invention, in general, relates to a radio frequency identification transponder and, more particularly, to a radio frequency identification transponder antenna.
Radio frequency identification, hereafter sometimes referred to as “RFID” makes it possible without physical or visual contact to read and store physical data and in the context of the instant invention will be understood generically to refer to a complete technical infrastructure. As a rule, a RFID system includes a transponder, also known as a tag or smart label, a transmission and receiving unit und their integration into servers, services and other systems. It is the transponder to which the instant invention relates.
2. The Prior Art
RFID transponders including a microchip, a resonant structure and an impedance matching structure are well known in the art. Usually, the transponder is connected galvanically with the resonant and impedance matching structures.
The purpose of the impedance matching structure is to tune the value of the base or termination impedance of a transponder antenna to the input impedance of the transponder chip and thus to ensure an optimization of the transmission of energy. To this end, the prior art utilizes inductively acting antenna elements of the kind described by Constantine Balanis in “Antenna Theory” (John Wiley & Sons, 1997) or by John Kraus and Ronald Marhefka in “Antennas for all Applications” (McGraw Hill 2002).
Together, the microchip and the resonant structure constitute the RFID transponder, and in the prior art the impedance matching takes place within the resonant structure. U.S. Pat. No. 6,285,342 B1 discloses a RFID transponder provided with a miniaturized resonant antenna.
The drawback of such prior art devices is that the desired optimum matching of the microchip to known structures is not only complex in terms of process and fabrication, but also, and because of it, expensive. The fabrication of the transponder necessitates high geometric precision which leads to substantial complexities in the relatively large structures.
Another disadvantage of prior art devices is the likelihood of the microchips being damaged or destroyed when exposed to electrostatic discharges. The useful life and proper functioning of the transponders are, therefore, negatively affected and at best uncertain.